1. Field of the Invention
The present invention relates, in general, to analytical devices and, in particular, to microfluidic analytical systems.
2. Description of the Related Art
In analytical devices based on liquid samples (i.e., fluidic analytical devices), the requisite liquid samples should be controlled with a high degree of accuracy and precision in order to obtain reliable analytical results. Such control is especially warranted with respect to “microfluidic” analytical devices that employ liquid samples of small volume, for example, 10 nanoliters to 10 microliters. In such microfluidic analytical devices, the liquid samples are typically contained and transported in micro-channels with dimensions on the order of, for example, 10 micrometers to 500 micrometers.
The control (e.g., transportation, position detection, flow rate determination and/or volume determination) of small volume liquid samples within micro-channels can be essential in the success of a variety of analytical procedures including the determination of glucose concentration in interstitial fluid (ISF) samples. For example, obtaining reliable results may require knowledge of liquid sample position in order to insure that a liquid sample has arrived at a detection area before analysis is commenced. The relatively small size of the liquid samples and micro-channels in microfluidic analytical devices can, however, render such control problematic.
In the context of analytical systems for blood glucose monitoring, continuous or semi-continuous monitoring systems and methods are advantageous in that they provide enhanced insight into blood glucose concentration trends, the effect of food and medication on blood glucose concentration and a user's overall glycemic control. A challenge of continuous or semi-continuous glucose monitoring systems is that only small volumes of liquid sample (e.g., an ISF liquid sample of about 250 nanoliters) are generally available for measuring a glucose concentration. In addition, it is difficult to transport small volumes of liquid from a target site to an ex vivo glucose monitor with a controlled flow rate and in such a way that the position and total volume of extracted fluid is known.
Still needed in the field, therefore, is a microfluidic analytical system that enables small volume liquid sample control and otherwise alleviate the problems described above.